FIELD OF THE INVENTION
The invention relates to a turbine shaft of a steam turbine, in particular for accommodating the high-pressure and intermediate-pressure blading, and also to a method of cooling the turbine shaft of a steam turbine.
The use of steam at higher pressures and temperatures helps to increase the efficiency of a steam turbine. The use of such steam imposes increased requirements on the corresponding steam turbine. A single-line steam turbine having a high-pressure turbine section and an intermediate-pressure turbine section as well as a downstream low-pressure turbine section is suitable in the case of a steam turbine in a power range of several 100 MW. Both the high-pressure moving blades and the intermediate-pressure moving blades are accommodated by the turbine shaft, which if need be is composed of a plurality of segments. Each turbine section may have an inner casing and an outer casing, which in each case are, for example, split horizontally and bolted together. The live-steam state characterized by the high-pressure steam may be at around 170 bar and 540.degree. C. In the course of increasing the efficiency, a live-steam state of up to 270 bar and 600.degree. C. may be aimed at. The high-pressure steam is fed to the turbine shaft and flows through the high-pressure blading up to a discharge connection. The steam expanded and cooled down in the process may be fed to a boiler and heated up again there. The steam state at the end of the high-pressure turbine section is designated below as "cold reheating", and the steam state after leaving the boiler is designated below as "hot reheating". The steam issuing from the boiler is fed to the intermediate-pressure blading. The steam state may be around 30 bar up to 50 bar and 540.degree. C., an increase to a steam state of about 50 bar up to 60 bar and 600.degree. C. being aimed at. In a steam-inflow region, in particular of the intermediate-pressure turbine section, configuration measures in which the turbine shaft is protected from direct contact with the steam via a shaft screen may be carried out.
In Published, Non-Prosecuted German Patent Application DE 195 31 290 A1 there is specified a rotor for thermal turbo-engines, containing a compressor part, disposed on a shaft, a central part and a turbine part. The rotor is made up predominantly of individual welded-together bodies of rotation, the geometrical shape of which leads to the formation of axially symmetrical cavities between the respectively neighbouring bodies of rotation. The rotor has an axially directed cylindrical cavity, reaching from the end of the rotor on the inflow side to the last cavity on the upstream side. Placed in this cylindrical cavity are at least two tubes of diameters and lengths differing from one another. This is intended to allow the rotor of the turbo-engine to be brought to its operating state within the shortest time and to be easy to regulate thermally, i.e. according to requirements, heatable or coolable with relatively little effort.
U.S. Pat. No. 5,054,996 concerns a gas turbine rotor containing rotor discs interconnected by an axial tie rod. Air is directed through the gas turbine rotor, whereby the rotor and the rotor discs are heatable and coolable essentially uniformly.
U.S. Pat. No. 5,498,131 discloses a steam turbine installation with a system for reducing thermomechanical stresses, which may occur in a turbine shaft during the starting up or shutting down of the steam turbine installation. For this purpose, the steam turbine installation has a high-pressure turbine section and an intermediate-pressure turbine section with a single turbine shaft, which has a central bore passing right the way through. The central bore can be supplied with steam via a separate supply system for steam, respectively outside the casing of the turbine sections, during the starting up or shutting down of the steam turbine installation. Between the two turbine sections, i.e. approximately at the center of the turbine shaft, the steam is discharged again from the central bore. The system makes it possible for the transient starting-up or shutting-down state to be passed through in a short time in an improved and controlled manner.
In Patent Abstract of Japan N-303, Jun. 20, 1984, Vol. 8, No. 132, relating to Japanese Patent Application JP-A-59-34402, there is described a turbine shaft for a steam turbine. This turbine shaft of a single steam turbine has in its interior an axial bore, into which there is centrally introduced a cooling fluid, which flows out again on both sides at the ends of the bore.